Problematic with such compressed air radial motors is, among other things, the requirement of a sealing contact which seals as tightly as possible between the standing-still contact surface of the control head and the rotating contact surface of the supporting disc in order to avoid pressure loss of the pressure medium, which is diametrically opposed to a low-frictional performance to avoid torsional losses.
Attempts to press the control head onto the support disc by means of spring means or, for instance, in accordance with CH Patent No. 584,857 using bellows means failed not only because of the necessary technical resources but in particular because of the completely insufficient torque, particularly at low rotational speed, as a result of the friction load between the contact surfaces of the rotatably-fixed control head and the rotating support disc.